In a known device of this kind, disclosed in German Offenlegungschrift Pat. No. 2,244,638, the band carriers are pivotally installed, being in the form of flaps, and are pre-stressed by means of a spring. A special press-on finger which has co-ordinated with it a reciprocating entraining device, is incorporated to hold the band fast on the flaps.
It is an object of the invention to simplify a device of the kind described and thereby to render the same more reliable in operation.